Electrostatic reproducer



Dec. 3o, w30.

AR.' H. LEFFLER ELECTROSTATIC REPRODUCER Filed Jan. 18, 1929 Patented Da. 30, 193e l 1,736,436

UNITED STATES PATENT OFFICE RALIH H. LEFFLEB, F BA'IAVIA, ILLINOIS ELECTBOSTATIC REPRODUCER Application led January 18, 1929. Serial No. 333,492.

The present invention relates to an electroplates longitudinally to the vibratory plates. static reproducer for the reproduction of Another object of the present invention is phonograph records and the like and has to to provide means for adjusting the spacing do with an improved mechanism for the elecof stationary plates in a condenser reprotrical reproduction of such records. ducer transversely relative to the length of 55 One object of the present invention is to a vibratory plate therein. provide a reproducer of the electrical cony Another object ofthe present invention is denser type in which there are no coils of to provide means for adjusting the thickness copper or other wire, iron cores, or permanent of an air gap dielectric between the faces of magnets. Thus eddy current losses, hysterstationary plates and the co-operating vibra- 60 esis losses, and the eli'ect of saturation, all tor plate in a condenser reproducer.

of which are inherent to electrical repro nother object of the present invention is ducers of the magnetic type, are eliminated to provide a mechanical structure for a viand improved reproduction obtained. bratory plate, fulcrum, stylus, and adjusting Another object of the present invention is element in a reproducer such that the total to provide a reproducer of the electrostatic mass, and consequently the mechanical intype in which the vibrations of one plate reertia thereof, is reduced to a minimum. act electrically upon fixed plates on opposite The principal object of the present invensides of said vibratory plate, such reproducer tion is to provide an electrical reproducer operating in conjunction with a special vachavin qualities of reproduction superior to uum tube circuit in which advantage is taken that o tainable from reproducers of the magof the inverse capacitance variation thus obnetic type, and to that of heretofore designed tained to produce a cumulative eiect in the reproducers ofthe condenser type. output of the said vacuum tube circuit. Sub- These, and such other objects as may here- '.25 stantially double the effect may be obtained' inafter appear, are obtained from the novel 75 from unit motion of the vibratory member combination, unique construction and imin such an arrangement over that which may proved arrangement of the elements incorbe obtained when a single stationary plate porated into the one form of the present infunctions in conjunction with a vibratory vention disclosed in the accompanying single 3 plate. sheet of drawing hereby made a part of this Another object of the present invention is specification. to provide a symmetrical mechanical arrange- In said drawing: ment for the vibratory and stationary plates Figure 1 is a schematic representation, in of such a reproducer. y cross-section, of the spaced positions of two Another object of the present invention is fixed condenser plates relative to vibratory to provide equal damping effects upon oppoparts including a plate, a Julcrum, and a site sides of a vibratory plate longitudinal to stylus; the direction of motion. Figure 2 is a schematic side elevation illus- An additional object is to provide means trating the relative proportions ofthe vibra; 40 for mountingavibratory plate inconjunction tory parts comprising a plate, a fulcrum, a

with a stylus whereby to cause in such vibrasetscrewl,and.a stylus; tory plate a large volume of motion relative Figurey 3 is an end ele-vation of the vibrato unit motion of the stylus. j, tory plate shown in Figure 2 and in con- Another object of the present invention is junctlon with F igurel 2 illustrates the means to provide means for insulating acoustically employed to reduce the mass of the vibratory from the stationary parts of a reproducer the parts, and consequently the mechanical invibratory parts thereof. ertia thereof, to a minimum.

A further object of the present invention is j Figure 4 is a cross-section. through a conto provide in an electrostatic reproducer denser-reproducer illustrating means emv means for adjusting the spacing of stationary ployed to adjust the thickness of the air gap fil dielectric between stationary plates and a vibratory plate associated therewith, also means to adjust said stationary plates longitudinally to the length of the vibratory late p Figure 5 is a transverse cross-section in the line 5-5 of Figure 4, looking in the direction of the arrows.

Figure 6 is a vertical section illustrating in detail means employed to insulate acoustically the fulcrum of vibratory parts from the main body of a reproducer by the use of damping materials and also shows means employed to vary the tension upon the fulcrum by an adjusting member in conjunction with its locking device;

Figure 7 is a front elevation schematically illustrating in detail one means employed to obtain equal damping effects on opposite sides of a vibratory plate longitudinal to the direction of motion.

Figure 8 is a side elevation illustrating the means upon the stationary plates to adjust the spacing between said stationary plate and the vibratory plat transversely of the vibratory plate; and

Figure 9 is a schematic representation of a circuit in which such a reproducer may be employed.

That portion of the reproducer which is associated with the grid circuit shifts the frequency of the oscillator with variations in the capacitance, while that portion associated with the anode circuit causes a shift in the resonant point of the modulating circuit, the combined effects being so phased that the re- `sultant currents are cumulative in so far as the currents flowing in the anodecircuit arel concerned.

Like reference characters are used to indicate similar parts in the drawing and in the hereinafter given description of the apparatus. y

In the present invention there is an improved electrostatic reproducer having no coils, permanent magnets, or magnetic circuits of any kind. As is shown schematically in Figure 17 the fundamental elements of such condenser reproducer-comprise fixed metallic plates, 1 and 2, and a movable or flexible metallic plate 3. These plates form an electrostatic condenser, the air gap between the several plates being the dielectric.

As is well known, the capacitance of an electrical condenser is an inverse function of the depth or thickness of the dielectric between the conducting plates which it separates. This being t-rue, it is to be observed that as plate 3 is made to move towards the right (of Figure 1) by a stylus 5 actin upon a fulcrum 4, as when the stylus 5is ollowing the groove 39 of a phonograph record, the capacitance between 1 and 3 1s made to increase while the capacitance between 2 and 3 is made to decrease at exactly the same rate because the movable plate 3 is located between the two fixed plates 1 and 2. This statement assumes for predication, of course, that the movable plate 3 is located midway between and its faces are parallel to plates 1 and 2, resulting normally in equal air gap dielectrics at each side of plate 3.

When the motion of plate 3 is towards the left, the effect is exactly the opposite to that above described, that is, the capacitance between plates 2 and 3 increases while that between plates 1 and 3 decreases. Thus, as the stylus 5 passes along the groove 39 of a phonograph record, capacitance variations occur in the reproducer at nearly the same rate as the rate of change of curvature of the groove 39 of the phonograph record.

The amount of deviation from a linear capacitance to motion rate of change is governed, among other factors, by the amount of the non-parallelismbetween the stationary and the moyable plates. These capacitance variations may be made to cause a similar rate of change in an electric current in a suitably designed amplifier circuit, and thus a high quality of reproduction is obtained.

It. is to be further observed that the two y fixed metallic plates 1 and 2 are not in metallic connection with one another, but are kept 'electrically separate, thus forming with plate 3, in reality, two small variable condensers, one comprising the plates 1 and 3, and the 'other the plates 2 and 3. These two variable condensers may be connected in a vacuum tube circuit in such a way that their inverse capacitance variations produce a cumulative effectin the output circuit. (See applicants heretofore filed application for Letters Patr. ent, Serial Number 309,551, filed October 1, 1928, entitled Amplifying system, andFigure 9 of the drawing in this application.)

Reference should now be had to the vibratory parts shown in Figures 2 and 3. By the struct-ure shown, a relatively large amount of mechanical motion'of a movable plate 3 relative to the motion of a stylus 5 is obtained. The pivot or fulcrum of motion is at 4, close to the point 36 of the stylus 5, the fulcrum 4 is small in comparison with the distance from the fulcrum 4 to the other end of plate 3.

Thus, a lever multiplying action is obtained and-therefore a small amount of motion at the stylus point 36 produces a much greater movement of plate 3, and consequently results in large capacitance variations in the condensers formed by plates 1 and 3, and plates 2 and 3, and this results in a large current variation and volume of sound output in av suitable circuit in which the device is employed, as for example, that shown in Figure 9.

For the purpose of supporting the two condensers or double condenser of the herein only is illustrated in Figure 5, which comprises a cross-section through such a frame or housing andillustrates and discloses in conjunction with Fi ures 5, 6, 7 and 8, the relationship existing etween the various condenser parts and the stylus.

Any suitable configuration may be ado ted for the housing of the condenser. Li ewise any satisfactory combination of parts maybe employed for forming such housing. The shape or style of the housing is immaterial. Any device which holds the required parts, only one form of which is here shown, will suffice.

In that form of housing illustrated in Figure 4 there are side ieces, 40 and 41, and a top member 42 and a ottom member 43. Intermediate the side members 40 and 41 and the top and bottom members, 42 and 43, there are connecting-means. illustrated in the accompanying drawing as screws. ln the bottcm member 43, there is an aperture 44 through which access is had to the inside of the housing or frame and it is through this aperture that the movable. condenser plate 3 and its associated parts is inserted.

The mounting for such movable condenser plate is secured at the bottom of said housing, and the mounting therefor, best illustrated in Figure 6 is adapted to be attached thereto by a plurality of screws or other suitable fastening members 44 and 45.

Within the housing, the fixed plates 2 and 3 are disposed, each being situated substantially equidistantly from the side members 40 and 41. To obtain an adjustment toward and away from the movable condenser element, each fixed condenser plate is mounted upon a carrier block 46. Such carrier block has two threaded apertures 47 in the top thereof, and another48 in the bottom thereof. 1

From the sides 40 and 41 of the device to'and' into each aperture, a machine screw 49 is disposed. Blocks of insulatory material, such as for example, blocks 10 and 11 may be attached to the side members 40 and 41. About the shank of such screw and intermediate the internal surface of the side members 4() and 41 or of blocks 10 and 11 and the block 46, is a helical spring 50 whereby said'block is urged away from said sides 40 and 41 or insulatory blocks 10 and 11 at all times.

By rotation of the screws k49, the .blockmay be regulated by the adjustment of screws 49 until such relation as is required is secured.

Referring now to Figure 7, 1t will be seen that there are at the tcp of the frame adjusting screws 12 and 13 which engagea damplng material 8 and 9, or any other suitable material may be employed, which material in turn is in contact with the tip of said movable plate 3. This provides the major portion of the damping impedance. Additional damping impedances are obtained from the compression forces resulting from the movable plate 3 acting upon the relatively thin sheet of air dielectric which exists between the fixed and movable plates .1', 2, and 3.

ing in improvedreproducing qualities of tone reproduction.

Bushings 18 and 19 which surround the fulcrum 4 absorb such motion and these bushings also center the vibratory parts in their normal position. Bushings 18 and 19 are seated in a body member 20 which is adjustably mounted upon the frame, thereby providing means for producing the requisite tension upon the fulcrum. Set screw 21 and screw 22 passing through body 20 and bottom member 43 maintain body 2() in a fixed position upon said frame and said set screws 21 and 22 maintain the body 20 in position after once adjusted relatively to the frame.

Referring again to Figure 4. which should be read in conjunction with Figure 7, it is to `be again noted that the plates 1 and 2 are mounted upon electrical insulating blocks 46. Means have already been described whereby said blocks 46 with their attached metallic plates 1 and 2 may be adjusted to any position and spacing relative to the movable plate 3 by the use of adjusting screws I49.in conjunction with the compressionsprings 50.

Figure 8 discloses how the three adjusting screws 49 are spaced in the corners of a triangle when viewed from the side of the reproducer. By virtue of the triangular arrangement of the adjusting screws 49, the insulating blocks 46 together with their metallic plates 1 and 2, may be tilted to any desired position relative to the movable plate 3 in addition gto being moved toward and away therefrom. This tilting adjustment provides means for obtaining a large variation in the percentage change in the capacitance relative to motion, thereby producing quality variations in the sound out-` ut. p In eheh of the drawings, the screw for holding the needle is indicated by the numeral 50 The stylus or needle 5 is connnected toA embodied in the present invention is use to cause a shift in the frequency of a radiofrequency oscillator. Such shift in fre- Vquency at either a constant or at a variable rate causes a large variation in the anode current of the associated vacuum tube, the current changing at a predetermined rate relative to the shift in the frequency of the radiofrequency oscillator.

Figure 9 illustrates such a modified type of circuit adapted to be employed for phonoaphic record reproduction with the conenser pickup illustrated in the dpreceding figures. In said Figure 9, the con enser element herein described and illustratedl is indicated by three plates crossed by an arrow.

In Figure 9, xed condenser lates 1 and 2 are disposed at opposite side o said movable condenser plate and are diierentially connected to the electrical circuit there "shown.

One of the fixed plates of the reproducer is connected to a circuit in which is disposed a fixed condenser C, such circuit terminating intermediate a choke-coil and the modulatin circuit electrically connected to the plate o l a vacuum tube.

The other fixed plate of the reproducer is electrically connected to the dgrid circuit of said-vacuum tube. Said gri circuit is biased by a battery, and is electricall connected through the filament circuit to t e movable condenser plate, there being rinductance L 1n said grid circuit, the coil extendin across from the movable plate to the fixed p ate last mentioned.

The plate circuit of such reproducing circuit is a tuned plate modulating circuit having in one side thereof `inductance L and in the other side thereof, a capacity VO.

Disposed in the circuit is a choke-coil marked ChokeJ and a .plate circuit battery. A variation in the frequencyof the oscillator coincident with movements of the movable condenser element 3 relative to the fixed condenser elements 1 and 2 produces augmented variation in the plate current, and these variations in the Vplate current affect the audiofrequency transformer T therein and, of course, the output of the circuit.

The movable c'ondenser plate 3 is preferably of a type adapted to be flexed by moveinsane ment of the stylus 5, rather than one whichI will moveupon a pivot or about a trunion be so arranged and a portion only thereof 1s flexed as incident to movement of the stylus 5;

This articular feature of the invention is not limited in its utilities to an electrostatic' reproducer but, on the other hand, may be employed with success with a magnetic reproducer.

Likewise, such structure may be made a part of a single plate vibratory condenser, or a condenser having one fixed plate and one flexible late, or a device having a lurality of iexib e plates in con'unction wit a fixed late, or a plurality o fixed lates in con- ]unction with a single ilexib e plate, or a plurality of flexible plates in cooperation with a plurality of fixed plates. The advantages by employing a plate which will flex, rather than one which is moved b the stylus, is that the ad'ustment of such a iiyexible plate is maintaine over a greater period of time,

and there is greater truthfulness in re rov duction, it being possible to control to a er de ree the flexin movement of such a plate guided by a sty us. Ofu course, the movements of the plate are minute, and are rapid,

so that much is gained by providing a mount'- ing requiring the material of the plate to be flexed rather than to move about a point or pivot.

I' claim:

1. An electrostatic reproducer for the reproduction of records comprising a exible metallic plate associated with fixed metallic plates to form several variable capacity ele ments, said flexible plate being mounted at its ends beyond said fixed plates, the bod of said flexible lplate being between said Xed metallic plates in such a manner that inverse capacitance variations are produced simultaneously between said movable plate and said fixed plates by lateral movement of one of the extending ends of said flexible plate.

2. A condenser having a'movable metallic plate associated with a lixed metallic plate to provide variable capacitance and in which said movable plate is'flexed, and comprising a fixed late having aplurality of supports each adjustable to advance or retract a part of said fixed plate relatively to said movable plate, and damping means movable toward and away from said movable plate.

' 3 A'reproducer comprising a plurality of capacity elements having capacitances variab e inversely, simultaneously, and relatively to each other, having a movable metallic element associated with a fixed metallic element to provide variable capacitance, and in which said movable element is exed, and wherein there is a fixed plate having a plurality of supports each a instable to advance or retract a part of said fixed plate relatively to said movable element, and damping means movable towardand away from said movable element.

4. A reproducer of the electrostatic type for the reproduction of records comprising a movable member adapted to be flexed, one end thereof being disposed between damping means and the other seated in a housing, a plate at each side thereof, a housing for said plates andmember7 means in said housing for advancing or retracting said plates relatively to said movable member, and damping means adjustably disposed relatively to said movable member and in said housing.

RALPH H. LEFFLER. 

